Mechanical rectification involves converting reciprocating motion to either rotational motion or rectilinear motion. The classic mechanical rectifier is a piston/crankshaft mechanism. To produce mechanical advantage in the classic system, gearing and lubrication are required, thus making such a system unsuitable for applications requiring both a compact mechanism and a high degree of precision, such as robotics applications, e.g. prostheses and other high force-to-weight ratio applications. Such a system is likewise unsuitable for applications involving high-temperature or vacuum environments. Recently, however, vibratory motors, which may be well-suited to such applications, have been considered theoretically by R. W. Brockett in the paper entitled "On The Control of Vibratory Actuators", Proceedings of the 1987 IEEE Conference on Decision and Control, December 1987, pages 1418-1422, which is hereby incorporated by reference.
Linear motors employing piezoelectric transducers are described in a paper entitled "Present State of the Art of Ultrasonic Motors", by S. Uheha, Proceedings of the 9th Symposium on Ultrasonic Electronics, Sendai 1988 Japanese Journal of Applied Physics, Vol. 28 (1989) Supplement 28-1, pp. 3-6. Such motors rely on intermittent frictional contact between a rotor movable along a contacting surface and a vibrating stator, which is excited by piezoelectric elements, resulting in the propagation of a travelling wave along the contacting surface. The contacting surface of the motor follows an elliptic path which results in unidirectional motion. In a paper entitled "Hybrid Transducer Type Ultrasonic Linear Motor", by M. Kurosawa et al., Proceedings of the 9th Symposium on Ultrasonic Electronics, Sendai 1988 Japanese Journal of Applied Physics, Vol. 28 (1989) Supplement 28-1, pp. 158-163, a different mode of operation is described wherein piezoelectric transducers are employed directly as extenders and clamps in order to generate linear motion. Disadvantageously, since piezoelectric materials comprise the primary moving, or "working", elements of such motors, the power output capability is generally limited by the energy density and strain of piezoelectric materials.
Therefore, it is desirable to provide a new and improved linear motor that is practical for applications involving a wide range of load levels and is simple in construction.